In a prospective, nonrandomized study conducted between February 1997 and September 1998, 29 displaced fractures of the distal femur were stabilized with an angular stable interlocking plate system (Less Invasive Stabilization System [LISS] designed for minimally invasive placement. The LISS consists of an anatomically configured plate contoured to fit onto the lateral femoral condyle and fixed to the shaft with monocortical screws which interlock into the plate and build an angular stable plate/ screw construct. Using the AO fracture classification system, group 33C3 fractures and 33C2 fractures with intra-articular displacement were generally fixed with a transarticular approach with a lateral parapatellar arthrotomy of the knee joint and percutaneous placement of the shaft screws. While 33A type fractures and intra-articular nondisplaced group 33C2 and 32B1 fractures were treated with a lateral stab incision. The LISS was placed laterally on the femoral shaft under the vastus lateralis muscle.
Twenty-nine cases with an average age of 54 years (range, 20–92 yrs) were included; the mean follow up was 6 months (range, 1.5-16 mos). The mean Injury Severity Score was 14.1 (range, 9–27). Twenty-six fractures were located at the distal segment of the femur (localization 33), further subdivided into 13 group C3, four group C2 fractures, eight type A fractures, and one type B fracture. An additional three fractures were located at the distal shaft (localization 32) and classified as subgroup B13. Eight fractures were open (one type I, five type II, one type IIIB10,11). Mean operative time was 131 minutes (range, 40–300 min). Mean image intensifier time was 142 seconds (range, 31–402 sec). Postoperative complications included one case with heterotopic ossification (HO) limiting knee motion, one case of deep thrombosis with pulmonary embolism, and three cases of deep infection (one type IIIB open, one arterial injury, and one type II open). Implantand technique-related complications included two cases of proximal screw pull-out in the first 2 months post-injury. These cases were treated by proximal screw exchange. A rotational correction was performed in a 37-year-old woman with an increased antetorsion angle of 32° (internal rotation deformity) postoperatively.
Time to fracture healing averaged 3.1 months (range, 2.5 4–4.5 mos) in 23 cases. Time to full weight bearing averaged 3 months (range, 1.5-5 mos). At the latest follow up of 15 cases with more than 3 months' follow up, the knee flexion averaged 121° (minimum 20°, maximum 140°). Thirteen cases had a knee flexion of less than 120° with three of them less than 90°. In two cases at the follow up, an extension lag of 10° was noted. The Lysholm29 score was available for nine patients and showed a mean of 67.5 points (range, 48–92) and the Neer39 score for nine patients with follow up of more than 1 year averaged 69.8 points (range, 49–88; one failure, three unsatisfactory, four satisfactory, and one excellent result). The other cases were still under follow up with ongoing evaluations.
The use of the LISS for distal femoral fractures with correct technique lead to uneventful bony healing without the additional morbidity of a bone graft. However, the surgical technique is demanding and care must be taken to restore axial alignment..
© 1999 Lippincott Williams & Wilkins, Inc.